Liquid-encapsulated vibration-proof mount device

ABSTRACT

A vibration-proof mount includes an inner shell member comprised of a center pipe and a bush, and an outer shell member including a first collar and a second collar. The center pipe and the outer shell member are connected to each other by first and second elastomer members with a liquid encapsulated therein. A liquid chamber is formed between the first and second elastomer members and expanded and contracted in volume by a load, and an orifice is defined in the first elastomer member and connected to the liquid chamber. The orifice is formed by only a wall surface of the first elastomer member and hence, the sectional area of a flow path in the orifice can be insured to prevent a difference in characteristic between individuals of the vibration-proof mount, as compared with the case where the orifice is defined between a plurality of members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid-encapsulated vibration-proof mount device comprising an inner shell member disposed at a radially inner location of the mount device, an outer shell member disposed at a radially outer location of the mount device, a single or plurality of elastomer members in which a liquid is encapsulated, and an orifice formed in a flow path of the liquid, an outer peripheral surface of the inner shell member and an inner peripheral surface of the outer shell member being interconnected by the elastomer member.

2. Description of the Related Art

Such vibration-proof mount device is already known, for example, from Japanese Utility Mode Application Laid-open Nos.1-89644 and 1-113646.

However, the above known vibration-proof mount device has a problem that the orifice is formed as a gap between the elastomer member and a metal member. For this reason, an error is produced in the flow path sectional area of the orifice depending upon a combined state of the two members and therefore, a difference in characteristics is likely to be produced between individual vibration-proof mount devices.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to assure the accuracy of the flow path sectional area of the orifice to prevent the difference in characteristic from being produced between the individual vibration-proof mount device.

To achieve the above object, according to the present invention, there is provided a liquid-encapsulated vibration-proof mount device comprising an inner shell member disposed at a radially inner location of the mount device, an outer shell member disposed at a radially outer location of the mount device, a single or plurality of elastomer members in which a liquid is encapsulated, and an orifice formed in a flow path of the liquid, an outer peripheral surface of the inner shell member and an inner peripheral surface of the outer shell member being interconnected by the elastomer member, wherein the orifice is formed by a wall surface of the single elastomer member.

With the above construction, the orifice is formed by the wall surface of the one elastomer member and therefore, as compared with the case where the orifice is formed by a combination of a plurality of members, the accuracy of the flow path sectional area of the orifice can be enhanced to prevent the difference in characteristic from being produced between the individual vibration-proof mount devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the invention will become apparent from the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a front sub-frame of a vehicle;

FIG. 2 is an enlarged sectional view taken along the line 2--2 in FIG. 1;

FIG. 3 is a vertical sectional view of a vibration-proof mount;

FIG. 4 is a sectional view of the vibration-proof mount taken along the line 4--4 in FIG. 2;

FIG. 5 is a sectional view taken along the line 4--4 in FIG. 2;

FIG. 6 is a partially broken perspective view of the vibration-proof mount;

FIG. 7 is a view taken along the arrow 7 in FIG. 6;

FIG. 8 is a view taken along the arrow 8 in FIG. 6;

FIG. 9 is a view for explaining a drain passage;

FIG. 10 is a view illustrating a first assembling step;

FIGS. 11A and 11B are enlarged views of portions shown by 11A and 11B in FIG. 10;

FIG. 12 is a view illustrating a second assembling step;

FIG. 13 is a view illustrating a third assembling step;

FIG. 14 is a graph illustrating the variation in dynamic spring constant by the compression of a second elastomer member;

FIG. 15 is a graph illustrating the variation in dynamic spring constant by the use of a high-damping material for the second elastomer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a front subframe SF of a vehicle is formed into a substantially frame-shape and includes a front beam 1 extending in a lateral direction of a vehicle body, a left side beam 2_(L) and a right side beam 2_(R) extending rearwards from left and right opposite ends of the front beam 1, and a rear beam 3 connecting the left and right side beams 2_(L) and 2_(R) to each other. An engine (not shown) is supported on a left engine mount 4_(L) and a right engine mount 4_(R) at left and right opposite ends of the rear beam 3 through mount brackets 5_(L) and 5_(R) interposed therebetween. The engine is further supported by stoppers 6, 6 (the right stopper 6 is not shown) provided at left and right opposite ends of the front beam 1.

The left side of the front subframe SF is supported on a left side frame F_(L) by a first vibration-proof mount M₁ fitted into a cup-like holder 7 formed at the left end of the front beam 1, and second and third vibration-proof mounts M₂ and M₃ fitted into two cup-like holders 8 and 9 formed at the left end of the rear beam 3. The first, second and third vibration-proof mounts M₁, M₂ and M₃ and the cup-like holders 7, 8 and 9 are commonly clamped to a lower surface of the left side frame F_(L) by bolts 10 and nuts 11. At this time, tip ends of plates sandwiched between the first and third vibration-proof mounts M₁ and M₂ and heads of the bolts 10 are coupled to a vehicle frame (not shown) by bolts 14 and 15, respectively. A washer 16 is clamped between the second vibration-proof mount M₂ and a head of the bolt 10.

The right side of the front subframe SF is supported on a right side frame F_(R) by first, second and third vibration-proof mounts M₁, M₂ and M₃ (not shown) in the same manner as is the above-described left side. All six of the vibration-proof mounts M₁, M₂ and M₃ have the same structure, therefore, only the structure of the second vibration-proof mount M₂ as representative of them will be described.

As shown in FIG. 2, the bolt 10 for fixing the vibration-proof mount M₂ fitted into an accommodating recess 8₁ of the cup-like holder 8 with an open lower surface to the left side frame F_(L) is passed through a washer 16, the vibration-proof mount M₂, an opening 8₂ in the cup-like holder 8, an annular seal rubber 17, a bolt bore 18₁ in the left side frame F_(L), a reinforcing collar 19 and a bolt bore 18₂ in the left side frame F_(L), and threadedly engaged in the nut 11.

As can be seen from FIGS. 3 to 8, the vibration-proof-mount M₂ includes a stepped cylindrical center pipe 21 having a bolt bore 21₁ through which the bolt 10 is passed. An inner periphery of a first elastomer member 22 made of a rubber is coupled, by baking, to outer peripheries of an upper smaller-diameter portion 21₃ and a larger-diameter portion 21₄ of the center pipe 21 excluding a lower smaller-diameter portion 21₂. A pair of orifices 22₁, 22₁ with their lower ends opened and their upper ends closed are axially formed circumferentially with a phase difference of 180° in the first elastomer member 22. A pair of gas chambers 22₂, 22₂, with their upper ends opened and their lower ends closed, are axially defined radially outside of the pair of orifices 22₁, 22₁. A pair of radially resiliently deformable diaphragms 22₃, 22₃ are formed between the orifices 22₁, 22₁ and the gas chambers 22₂, 22₂. An outer periphery of the first elastomer member 22 is coupled to an inner periphery of the first substantially cylindrical collar 23 by baking.

When the orifice is formed by clearances between a plurality of members, there is a possibility that an error may be produced in sectional areas of a flow path in the orifice due to a number of causes, such as a misalignment of relative positions of these members. However, each orifice 22₁, 22₁ is defined by only the wall surface of the single first elastomer member 22. Therefore, there is no possibility of the error produced in sectional area of the flow path due to the misalignment of the relative positions of the members, and it is possible to prevent a difference in characteristic from being produced between individual vibration-proof mount devices M₂.

A second elastomer member 26 made of a rubber is insertedly formed so as to connect a lower end of a second substantially cylindrical collar 24 and a bushing 25. An outer periphery of the first collar 23 is fitted to an inner periphery of the second collar 24. The second collar 24 and the first collar 23 are integrally coupled to each other by caulking an upper portion of the second collar 24 inwards, while caulking an upper end downwards (see caulking portions a₁ and a₂) in a state in which the lower end of the first collar 23 is in abutment against a step 24₁ of the second collar 24. When the second collar 24 is made, the step 24₁ can be formed by drawing. An inner periphery of the bushing 25 is integrally coupled to an outer periphery of the lower smaller-diameter portion 21₂ of the center pipe 21 by press-fitting (see a press-fit portion b).

When the second collar 24 and the first collar 23 have been integrally coupled to each other and the bushing 25 and the center pipe 21 have been integrally coupled to each other in the above manner, the lower end of the first elastomer member 22 and the upper end of the second elastomer member 26 are brought into close contact with each other to define an annular liquid chamber 26₁ therein. The liquid chamber 26₁ and the orifice 22₁ are in communication with each other, and a closed space with a liquid is encapsulated therein is defined by the liquid chamber 26₁ and the orifice 22₁. An essential portion of the second elastomer member 26 connecting the lower portion of the second collar 24 and the bushing 25 to each other constitutes a rubber portion 26₈ which is deformable in a vertical direction. The rubber portion 26₈ defines a lower wall of the liquid chamber 26₁.

Different materials having different loss factors are used for the first and second elastomer members 22 and 26. Specifically, a low-damping material having a smaller loss factor (e.g., natural rubber NR) is used for the first elastomer member 22, and a high-damping material having a larger loss factor (e.g., a butyl rubber IIR) is used for the second elastomer member 26.

The center pipe 21 and the bushing 25 constitute an inner shell member of the present invention, and the first collar 23 and the second collar 24 constitute an outer shell member of the present invention.

Three legs 26₃ each having an annular projection 26₂ at its intermediate portion are projectingly provided on a lower surface of the second elastomer member 26 and are fitted into three locking bore 16₁ defined in the collar 16, respectively. When the collar 16 is assembled to the vibration-proof mount M₂, the legs 26₃ are fitted into the locking bore 16₁ in the collar 16 and prevented from being falling off by the annular projections 26₂, whereby the vibration-proof mount M₂ and the collar 16 can be temporarily assembled, leading to enhanced workability.

As can be seen from a comparison between FIGS. 2 and 3, a seal lip 22₄ is projectingly provided on the upper end of the first elastomer member 22 to project above the upper end of the center pipe 21, and a seal lip 26₄ is projectingly provided on the lower end of the second elastomer member 26 to project below the lower end of the center pipe 21. In an assembled state shown in FIG. 3, the seal lip 22₄ of the first elastomer member 22 resiliently abuts against the lower surface of the left side frame F_(L) to exhibit a sealing effect, and the seal lip 26₄ of the second elastomer member 26 resiliently abuts against the upper surface of the washer 16 to exhibit a sealing effect.

Under the sealing effect of the seal lip 22₄ of the first elastomer member 22 abutting against the lower surface of the left side frame F_(L) and the sealing effect of the seal lip 264 of the second elastomer member 26 abutting against the upper surface of the washer 16, muddy water or the like is prevented from entering between the bolt bore 21₁ in the center pipe 21 and the bolt 10 to enhance durability against corrosion, but also the center pipe 21 and the bushing 25 are biased in directions to be press-fitted to each other by reaction forces received by the compressed seal lips 22₄ and 26₄ from the left side frame F_(L) and the washer 16. Therefore, looseness of the press-fit portion b is prevented. Moreover, by the fact that the seal lips 22₄ and 26₄ are integrally formed on the first and second elastomer members 22 and 26, a special seal member is not required, leading to a decrease in number of required parts.

Six annular ribs 26₅ having a triangular sectional shape are projectingly provided on the second elastomer member 26 covering the outer periphery of the second collar 24. The annular ribs 26₅ are cut away at locations corresponding to the radially outer portion of the gas chambers 22₂, 22₂, and two axially extending drain channels 26₆, 26₆ are defined in the cut-away portions. The annular ribs 26₅ have a function to decrease the area of the slide portion of the vibration-proof mount M₂ to facilitate the press-fitting operation, when the vibration-proof mount M₂ is press-fitted into the accommodating recess 8₁ in the cup-like holder 8.

As shown in FIG. 9, even if muddy water or other contaminant passed through the seal rubber 17 or the like enters into between the outer periphery of the second collar 24 and the inner periphery of the cup-like holder 8 for any reason, the muddy water will flow downwards through the drain channels 26₆, 26₆ in the annular ribs 26₅ and is discharged to the outside through three cutouts 26₇ defined in the upper surface of the lower portion of the second elastomer member 26. This avoids a disadvantage that the muddy water is accumulated between the vibration-proof mount M₂ and the cup-like holder 8 to generate a rust.

Steps of assembling the vibration-proof mount M₂ will be described below.

First, a first subassembly A₁ having the center pipe 21, the first elastomer member 22 and the first collar 23 integrally assembled together and a second subassembly A₂ having the second collar 24, the second elastomer member 26 and the bushing 25 integrally assembled together are previously assembled to each other, as shown in FIG. 10. In a state in which the lower portion of the second assembly A₂ has been fixed by a jig 28, the first subassembly A₁ is press-fitted into the second subassembly A₂ from above, as shown by arrows 29.

As can be seen from FIGS. 11A and 11B showing a portion shown by 11A and a portion shown by 11B in FIG. 10 in detail, lips L₁ and L₂ are projectingly provided on the second elastomer member 26 of the second subassembly A₂. The lips L₁ and L₂ are brought into abutment against the first subassembly A, press-fitted from above to achieve the sealing, so that the liquid inside is prevented from leaking. The step of fitting of the first and second subassemblies A₁ and A₂ is carried out in the liquid, but before the lip L₁ is brought into abutment against the first subassembly A₁, an extra portion of the encapsulated liquid is discharged to the outside through a very small gap between the first and second collars 23 and 24 (see arrows 30₁, 30₂ and 30₃ in FIG. 12).

At this time, the positioning of the first and second collars 23 and 24 is performed by abutment of the lower end of the first collar 23 against the step 24₁ formed in the middle of the second collar 24. The step 24₁ is simultaneously machined or worked in drawing the substantially cylindrical second collar 24 and hence, a special machining or working step is not required, leading to a decreased machining cost.

Then, the first and second collars 23 and 24 are integrally coupled to each other by caulking the upper portion of the second collar 24 at the caulking portion a₁ radially inwards and at the caulking portion a₂ downwards, as shown in FIG. 13. At this time, there is no possibility that the first and second collars 23 and 24 are misaligned due to a caulking load, because the relative positions of the first and second collars 23 and 24 are reliably defined by the step 24₁. Thus, it is possible to achieve an easy and precise assembling.

After completion of the fitting of the first and second subassemblies A₁ and A₂, the upper portion of the bushing 25 is fixed above the lower smaller-diameter portion of 21₂ of the center pipe 21 and hence, a vertical gap between the second collar 24 and the bushing 25 is shorter than that in a natural state (see character e in FIG. 10). This indicates that the mount M₂ has been assembled in a state that a vertical preload has been applied to the rubber portion 26₈ of the second elastomer member 26. Therefore, the vertical thickness of the rubber portion 26₈ is increased to increase the spring constant contributing to an increase and decrease in volume of the liquid chamber.

The operation of the vibration-proof mount M₂ having the above-described construction will be described below.

A large influence to the characteristic of orifice vibration system of the vibration-proof mount M₂ is exerted by springs of the diaphragms 22₃ and 22₃ formed on the first elastomer member 22, a spring of the rubber portion 26₈ formed on the second elastomer member 26 (a spring in expanding and contracting directions of the liquid chamber), and a mass of the liquid within the orifices 22₁, 22₁. The first elastomer member 22 constituting the upper wall of the liquid chamber 26₁ has an extremely large vertical thickness and is difficult to deform. Therefore, what largely contributes to the change in volume of the liquid chamber 26₁ is the deformation of the rubber portion 26₈ of the second elastomer member 26 constituting the lower wall of the liquid chamber 26₁ in the expanding and contracting directions of the liquid chamber. Therefore, the material of the second elastomer member 26 forming the rubber portion 26₈ is extremely important and thus, by using a high-damping material for the second elastomer member 26, the transmitting force of the vibration-proof mount M₂ can be decreased, and the durability of the diaphragms 22₃, 22₃ can be enhanced.

This will be described in detail with reference to FIG. 6. When a downward load F is applied to the center pipe 21 of the vibration-proof mount M₂ by the relative movement between the sub-frame SF and the left side frame F_(L), load F is transmitted to the second collar 24 as a load f₁ transmitted through the diaphragms 22₃, 22₃ and also to the second collar 24 as a load f₂ transmitted through the rubber portion 26₈. As a result, the downward deformation of the rubber portion 26₈ causes the volume of the liquid chamber 26₁ to be increased, and when the liquid is moved downwards slightly behind the increase in the volume (i.e., when the input frequency is slightly lower than a resonant frequency), a negative pressure is generated in the liquid chamber 26₁ to cause loads f₃ and f₄ to be applied to the upper and lower walls of the liquid chamber 26₁. Therefore, the upward load f₄ acting to eliminate the downward loads f₁, f₂ and f₃ causes the transmission of the load F from the center pipe 21 to the second collar 24 to be reduced.

To effectively generate the negative pressure in the liquid chamber 26₁, it is desirable that the rubber portion 26₈ opposed to the liquid chamber 26₁ is moved without being flexed upwards along with the center pipe 21, rather than being easily flexed upwards. For this purpose, the high-damping material difficult to be deformed by the liquid pressure is used for the second elastomer member 26. Thus, the dynamic spring constant. can be reduced, thereby providing the high-performance vibration-proof mount M₂ to which a vibration is difficult to be transmitted.

Because the shapes of the first and second elastomer members 22 and 26 are different, the first elastomer member 22 causes a surging in a relatively high range of input frequency, and the second elastomer member 26 causes a surging in a relatively low range of input frequency, and the dynamic spring constant is suddenly increased in these ranges, as shown in FIG. 14, resulting in a reduced performance. Therefore, by using the high-damping material for the second elastomer member 26, the deterioration of the dynamic spring constant can be suppressed to the minimum in an intended range of frequency, as shown by a dashed line. Particularly, the surging frequency range for the second elastomer member 26 having the large radial thickness is a range commonly used in a vehicle and hence, the suppression of the deterioration of the dynamic spring constant in such range can contribute to an enhancement in noise-vibration performance.

Although the high-damping material is used for the second elastomer member 26 in this embodiment, this is because the spring constant contributing to the variation in volume of the liquid chamber in the rubber portion 26₈ is several times larger than the spring constant of the diaphragms 22₃, 22₃.

Even when an upward load F' is applied to the center pipe 21 of the vibration-proof mount M₂ by the relative movement between the sub-frame SF and the left side frame F_(L), a positive pressure can be efficiently produced in the liquid chamber 26₁ to reduce the transmission of the upward load F' by the orifice effect, by the use of the high-damping material difficult to be deformed for the second elastomer member 26.

Further, if a low-damping material easy to be deformed is used for the second elastomer member 26, when the volume of the liquid chamber 26₁ is expanded or contracted, the rubber portion 26₈ forcibly pushes-out, or draws-in the liquid in the orifices 22₁, 22₁ and for this reason, there is a possibility that the amount of deformation of diaphragms 22₃, 22₃ having a smaller thickness is increased to reduce the durability. However, such disadvantage is eliminated by using the high-damping material for the second elastomer member 26.

As described above, by using the different materials having the different loss factors for the first and second elastomer members 22 and 26, the dynamic spring constant in the intended input frequency range can be tuned to any value.

An effect will be described below which is provided by press-fitting of the bushing 25 into the center pipe 21 to increase the spring constant of the rubber portion 26₈ of the second elastomer member 26.

A resonant frequency f provided by the orifice portions of the vibration-proof mount M₂ is given according to the following equation:

    f=(1/2π)×(k/m).sup.1/2

wherein m represents a mass of the liquid in the orifices 22₁, 22₁, and k represents a total spring constant of the first and second elastomer members 22 and 26 applied to the liquid in the orifices 22₁, 22₁. Therefore, the total spring constant k is increased by an increase in spring constant of the rubber portion 26₈ of the second elastomer member 26 as a result of press-fitting of the bushing 25, causing the resonant frequency f to be shifted toward a value higher than an input frequency range usually used. Therefore, a vibration-proof range in the input frequency range can be widened to enhance the riding comfort (see FIG. 15). Moreover, only by changing the shape of the second elastomer member 26 before being assembled to change the amount of compression of bushing 25 when being press-fitted, the spring constant can be easily regulated, leading to an extremely low cost.

In addition, the center pipe 21 is biased downwards and the first and second collars 23 and 24 are biased upwards, by a resilient force by which the compressed second elastomer 26 is intended to be restore to its free state (see an arrow A and an arrow B in FIG. 13). Therefore, a preload in the compressing direction can be applied to the diaphragms 22₃, 22₃ of the first elastomer member 22. As a result, the maximum amount of diaphragms 22₃, 22₃ elongated when being expanded is suppressed, leading to an enhanced durability of the diaphragms 22₃, 22₃.

Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims.

For example, the elastomer structure is formed from the two members: the first and second elastomer members 22 and 26 in the embodiment, but it may be formed from a single member or three or more members. 

What is claimed is:
 1. A liquid-encapsulated vibration-proof mount device comprising an inner shell member disposed at a radially inner location of the mount device, an outer shell member disposed at a radially outer location of the mount device, and first and second elastomer members defining a space therebetween in which a liquid is encapsulated, said space providing a flow path of said liquid and including an orifice formed in said flow path and a liquid chamber communicated with said orifice, an outer peripheral surface of said inner shell member and an inner peripheral surface of said outer shell member being interconnected by said first and second elastomer members,wherein said first elastomer member is coupled at an inner peripheral portion thereof to said outer peripheral surface of said inner shell member and at an outer peripheral portion thereof to said inner peripheral surface of said outer shell member, said first elastomer member having a diaphragm extending substantially axially of said inner and outer shell members with spacings from said inner and outer peripheral portions of the first elastomer member, respectively; and wherein said orifice is formed between said diaphragm and said inner peripheral portion of said first elastomer member.
 2. The device according to claim 1, wherein said inner shell member comprises a substantially cylindrical member and a bushing member coupled to one end portion of said substantially cylindrical member, and said outer shell member comprises a first substantially cylindrical collar and a second substantially cylindrical collar, said first and second collars being fixed relative to each other in axial directions thereof, and wherein said first elastomer member is coupled between said first substantially cylindrical collar and said substantially cylindrical member and said second elastomer member is coupled between said second substantially cylindrical collar and said bushing member.
 3. The device according to claim 1, wherein a gas chamber is defined between said diaphragm and said outer peripheral portion of said first elastomer member, said gas chamber being connected to the outside of the mount device.
 4. The device according to claim 2, wherein a gas chamber is defined between said diaphragm and said outer peripheral portion of said first elastomer member, said gas chamber being connected to the outside of the mount device.
 5. The device according to claim 1, wherein said orifice is formed as a pair of orifices arranged in a diametrically opposed fashion around said inner shell member.
 6. The device according to claim 2, wherein said orifice is formed as a pair of orifices arranged in a diametrically opposed fashion around said inner shell member. 